Methods of photocuring and imaging

ABSTRACT

The photocuring efficiency of a photoinitiator is increased by mixing it with an organic phosphite and an aldehyde. This mixture or photoinitiator composition can be used to cure acrylates or other photocurable compounds, particularly in an oxygen-containing environment.

FIELD OF THE INVENTION

This invention relates to methods for curing photocurable compositionsusing actinic radiation. In particular, the methods can be carried outin the presence of oxygen. In addition, this invention provides methodsfor imaging by photocuring the photocurable compositions.

BACKGROUND OF THE INVENTION

Natural and synthetic polymers have served essential needs in society.However, in recent times synthetic polymers have played an increasinglygreater role, particularly since the beginning of the 20th century. Suchsynthetic polymers are commonly prepared by an addition polymerizationmechanism, that is, free radical chain polymerization of unsaturatedmonomers. The majority of commercially significant processes are basedon free-radical chemistry, or chain polymerization that is initiated bya reactive species, which often is a free radical. The source of thefree radicals is termed an initiator or photoinitiator.

Photochemically induced polymerization reactions have become of greatimportance in industry, in particular for rapid curing of thin films,such as, for example, in the curing of paint coatings and plasticcoatings on paper, wood, metal, and plastic or in the drying of printinginks. This curing by irradiation in the presence of photoinitiators isdistinguished, compared with conventional methods for the drying orcuring of coatings, by saving of materials and energy, low thermalstress of the substrate, and in particular a high curing rate. Moreover,the preparation of polymer materials by polymerization of thecorresponding unsaturated monomeric starting materials is often carriedout photochemically and by means of photoinitiators in such conventionalprocesses as solution and emulsion polymerization. Since in thereactions mentioned, none of the reactants is usually capable ofabsorbing a sufficient amount of the photochemically active radiation,it is necessary to add photoinitiators.

Improvements in free radical chain polymerization have been focused bothon the polymer being produced and the photoinitiator. Whether aparticular unsaturated monomer can be converted to a polymer requiresstructural, thermodynamic, and kinetic feasibility. Even when all threeproperties are present, kinetic feasibility is achieved in many casesonly with a specific type of photoinitiator. Moreover, thephotoinitiator can have a significant effect on reaction rate, which, inturn, can determine the commercial success or failure of a particularpolymerization process or product.

The primary function of a photoinitiator is to generate free radicalswhen the photoinitiator is irradiated with light of appropriate energyor wavelength. Photoinitiators are classified into “Type I” (orphotocleavage) photoinitiators and “Type II” (or H-abstraction)photoinitiators according to the pathways by which the effectiveinitiating radicals are generated.

In contrast to photocleavage photoinitiators that are decomposed bylight directly into radicals that are effective in initiatingpolymerization, Type II photoinitiators require a hydrogen donor, ormore generally a source of abstractable hydrogen's in order to generateradicals that are effective in initiating polymerization. The process ofH-abstraction is usually a bimolecular reaction requiring the encounterof a photoinitiator and a hydrogen-donor. Any source of abstractablehydrogen's can be useful (for example, any structure that yields astable radical after H-abstraction may serve as an “H donor”) and suchsources include amines, thiols, unsaturated rubbers such aspolybutadiene or polyisoprene, and alcohols.

Type I photoinitiators can generate free radical either of the twofollowing mechanisms:

(1) the photoinitiator undergoes excitation by energy absorption withsubsequent decomposition into one or more radicals, or

(2) a sensitizer molecule absorbs light and the excited sensitizer thentransfers energy to the photoinitiator to generate free radicals.

The basic photochemistry and photophysics of both Type I and Type IIphotoinitiators have been well studied and utilized industrially in UVcurable systems (see for example, Turro, N.J., Modem MolecularPhotochemistry, 1991, University Science Books, chapters 7, 10, and13.).

A number of Type I photoinitiators are commonly used in a variety ofphotocuring related applications and are commercially available. AmongType I photoinitiators, the hydroxyalkylphenone photoinitiators haveproven to be particularly useful. Such photoinitiators include but arenot limited to, benzoin ethers, benzil monoketals,dialkoxyacetophenones, hydroxyalkylphenones, and derivatives derivedfrom these classes of compounds. α-Amino arylketones are also commonlyused as Type I photoinitiators and are commercially available as aremono-and bis-acylphosphine oxides.

Most known photoinitiators (both Type I and II) have only moderatequantum yields (generally less than 0.5), indicating that the conversionof light radiation to radical formation needs to be made more efficient.The overall efficiency of photocuring process, in addition to overallcomposition of polymerizable material(s), depends on the quantum yieldof radical generation of photoinitiator. To increase the overallefficiency of a photocuring, improvements in photoinitiators, as well asimprovements in photoinitiating compositions, are necessary. In somecases, the commercial viability of certain systems can depend on whethera relatively modest improvement, for example, in the 2 to 10 timesrange, can be achieved. Improving photocuring efficiency is especiallycritical since with increasing diversification and specialization ofprocesses and products in the area of coating techniques using polymermaterials and, more and more frequent requirement of providingtailor-made solutions for these problems, increasingly requires higherand more specific demands on the photoinitiators and photoinitiatingcompositions. Therefore, in many cases, known photoinitiators do notfulfill, or at least not to an optimum degree, the demand made on themtoday. In most practical applications major, problems include the needto achieve even maximum (or theoretical) photoinitiator efficiency.These problems arise, for example:

(a) due to inefficient light absorption in pigmented systems,

(b) lack of compatibility with a wide range of binder systems and theirreactive components and other modifying additives, or

(c) the storage instability in the dark of the systems containing thephotoinitiator and the possible deterioration in the quality of thecured final product, such as yellowing, as a result of unconvertedinitiator residues and initiator degradation products.

Besides these challenges, there is an additional challenge of freeradical photocuring inhibition by the presence of oxygen. Oxygeninhibition has always been a major problem for photocuring ofacrylate-containing compositions containing multifunctional acrylatemonomers or oligomers using a photoinitiated radical polymerization (forexample, see Decker et al., Macromolecules 18 (1985) 1241.). Oxygeninhibition is due to the rapid reaction of carbon centered propagatingradicals with oxygen molecules to yield peroxyl radicals. These peroxylradicals are not as reactive towards carbon-carbon unsaturated doublebonds and therefore do not initiate or participate in anyphotopolymerization reaction. Oxygen inhibition usually leads topremature chain termination, resulting in incomplete photocuring. Thus,many photocuring processes must be carried out in inert environments(for example, under nitrogen or argon), making such processes moreexpensive and difficult to use in industrial and laboratory settings.

Various methods have been proposed to overcome oxygen inhibition ofphotocuring:

(1) Amines that can undergo a rapid peroxidation reaction can be addedto consume the dissolved oxygen. However, the presence of amines inacrylate-containing compositions can cause yellowing in the resultingphotocured composition, create undesirable odors, and soften the curedcomposition because of chain transfer reactions. Moreover, thehydroperoxides thus formed will have a detrimental effect on theweathering resistance of the UV-cured composition.

(2) Dissolved oxygen can be converted into its excited singlet state bymeans of a red light irradiation in the presence of a dye sensitizer.The resulting ¹O₂ radical will be rapidly scavenged by a1,3-diphenylisobenzofuran molecule to generate a compound(1,2-dibenzoylbenzene) that can work as a photoinitiator (Decker,Makromol. Chem. 180 (1979), p. 2027). However, the photocuredcomposition can become colored, in spite of the photobleaching of thedye, prohibiting this technique for use in various products.

(3) The photoinitiator concentration can be increased to shorten the UVexposure during which atmospheric oxygen diffuses into the curedcomposition. This technique can also be used in combination with higherradiation intensities. Oxygen inhibition can further be reduced by usinghigh intensity flashes that generate large concentrations of initiatorradicals reacting with oxygen, but hydroperoxides are also formed.

(4) Free radical photopolymerization can be carried out under inertconditions (Wight, J Polym. Sci.: Polym. Lett. Ed. 16 (1978) 121), whichis the most efficient way to overcome oxygen inhibition. Nitrogen istypically continuously used to flush the photopolymerizable compositionduring UV exposure. On an industrial UV-curing line, which cannot bemade completely airtight, nitrogen losses can be significant, thusmaking the process expensive and inefficient. This is an even greaterconcern if argon is used to provide an inert environment.

Other less common ways of overcoming oxygen inhibition of acrylatephotopolymerization include using a wax bather and performing UVexposure under water. Each of these techniques has disadvantages thathave made them less likely for commercial application.

The use of phosphites as antioxidants and stabilizers in polymericcompositions is known. For example U.S. Patent Application Publication2004/0157949 A1 (Hu, [0058]) discloses the use of phosphites along withhindered amines and phenols as stabilizers in photocurable compositions.U.S. Patent Application Publication 2006/0173089 A1 (Jackson, [0026])discloses the use of phosphites, hindered phenols, and hindered amines,antioxidant stabilizers in radiation-crosslinked polyolefincompositions. This publication also teaches that the use of some ofthese antioxidants in “excessive amount” can act as “radiationscavengers” and thus reduce effectiveness of photocuring. U.S. PatentApplication Publication 2009/0292040 A1 (Sarmah) discloses the use ofphosphites and hindered phenols as antioxidants in radiation curableliquid resins. None of these publications suggests that phosphites canbe used with photoinitiators in photocurable compositions.

Phosphite stabilizers, for example, hindered neoalkyl phosphitecompositions as disclosed in U.S. Pat. No. 5,464,889 (Mahood) exhibitundesirable odors, which make their handling and processing unpleasantand perhaps hazardous. Reducing the odors of phosphites would be anadvance in the art for any use. It is clear from this discussion that inphotopolymerization technology, there are continuing opportunities forimprovements in free radical polymerization processes andphotoinitiators. Moreover, there is a need in the art for new,energy-efficient photoinitiator compositions that can be used for use ina variety of polymerization and photocuring processes in the presence ofoxygen. The need for highly efficient photoinitiating compositions isparticularly acute where absorption of light by the reaction medium maylimit the amount of energy available for absorption by thephotoinitiators. For example, in the preparation of color filterresists, highly pigmented resists are required for high color quality.With the increase in pigment content, the curing of color resistsbecomes more difficult. The same is true for the UV-photocurable inks,for example offset printing inks, which also are loaded with pigments.Hence, there is a need for methods of using photocurable compositionsthat have a higher sensitivity and excellent resolution properties andthat can be carried out in the presence of oxygen.

SUMMARY OF THE INVENTION

The present invention provides a method of photocuring a photocurablecomposition comprising:

mixing at least one photoinitiator, at least one organic phosphite, atleast one aldehyde, and at least one photocurable compound to form aphotocurable composition, and

irradiating the photocurable composition to provide a photocuredcomposition.

This invention also provides a method of imaging comprising:

A) providing a photocurable composition comprising at least onephotoinitiator, at least one organic phosphite, at least one aldehyde,and at least one photocurable compound to form a photocurablecomposition, and

B) imagewise irradiating the photocurable composition to effect a curedimage.

The present invention addresses some of the difficulties and problemsthat are discussed above with energy-efficient photoinitiatorcompositions that can be used in photocurable compositions and inmethods of photocuring in various industrial applications. One of theprimary advantages of the present invention is that when thephotoinitiator composition is combined with polymerizable orphotocurable materials, it provides more rapid curing times. Moreover,such rapid curing can be achieved in air or in the presence of oxygen aswell as in inert environments. Rapid curing in air is particularlyadvantageous since, as described above, oxygen usually inhibits curing.

The photoinitiator compositions used in this invention can generate freeradical species upon irradiation, for example under extremely low energylamps, such as excimer lamps and mercury lamps, as compared to knownphotoinitiators alone. Further, the photoinitiator and photocurablecompositions can be as much as 200 times faster that the best prior artphotocurable compositions.

At noted, when combined with a polymerizable or photocurable compoundsuch as an acrylate, the photoinitiator composition causes rapid curingtimes in comparison to the curing times with photoinitiator alone(without the organic phosphite). It was surprising to me that the use ofthe organic phosphite used in the photoinitiator and photocurablecompositions provided unexpectedly better performance in photocuringthan use of known Type I or Type II photoinitiators alone, even in thepresence of oxygen.

I have also found that combining an organic phosphite with an aldehydein the compositions of this invention surprisingly reduced unpleasantodors from the organic phosphites. Aldehydes, in equilibrium, are knownto form 1:1 adducts with phosphites (F. Ramirez, Pure Appl. Chem. 1964,9(2), 337-369). These 1:1 phosphite-aldehydes adducts could furtherreact with additional aldehyde to form cyclic tetralkoxyphosphoranes.Both 1:1 phosphite-aldehyde adducts as well as cyclictetralkoxyphosphorane are useful in the photocurable compositions. Inthe case of a molar excess of certain aliphatic aldehydes, 1:1, 1:2,1:3, or greater of phosphite-aldehyde adducts are possible (F. Ramirez,Pure Appl. Chem. 1964, 9(2), 337-369).

These and other features and advantages of the present invention willbecome apparent after a review of the following detailed description ofthe disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The photoinitiator compositions used in the present invention compriseat least one wavelength-specific photoinitiator, at least one organicphosphite compound, and at least one aldehyde. The photoinitiatorcompositions need no other components that are essential tophotoinitiation or the creation of free radicals. However, as notedbelow, the compositions can optionally include photosensitizers thatadjust or sharpen the spectral sensitivity of the photoinitiator tophotocuring radiation. Thus, addenda can be present that are not neededfor free radical generation but that relate to functions other thanphotoinitiating. A skilled worker would understand that with routineexperimentation, the combination of photoinitiator, organic phosphite,and aldehyde can be varied in type and amount of the compounds tooptimize the efficacy of photoinitiator composition with a givenphotocurable compound.

The present invention is useful in methods of polymerizing orphotocuring a photocurable compound, for example as part of an articleor in the formation of an article. For example, the photoinitiatorcompositions can be used in a method of photocuring or polymerizing oneor more ethylenically unsaturated polymerizable monomers, oligomers, orcrosslinkable polymers by exposing these photocurable compounds tosuitable radiation in the presence of the photoinitiator compositions.

The photoinitiator and photocurable compositions can be used to formfilms or coatings in articles, for example by providing a mixture of oneor more photocurable compounds and a photoinitiator composition as aphotocurable composition in a film or a coating and irradiating the filmor coating with a suitable amount of radiation sufficient to cure orpolymerize the film or coating. The photocurable composition can bedrawn into a film on a nonwoven web or into fibers.

Alternatively, the photoinitiator composition or photocurablecomposition can be applied in a suitable manner to a substrate prior tocuring by irradiation. Still again, a photocurable composition can beirradiating during the application to a substrate.

The photocurable compositions can also be used to form articles withadhesive compositions comprising a photocurable compound mixed with aphotoinitiator composition. Similarly, the present invention can be usedto form laminated structures (or articles) comprising at least twolayers bonded together with an adhesive composition, in which at leastone layer is a nonwoven web or film. Accordingly, the present inventioncan provide a way for laminating a structure having at least two layerswith the adhesive composition between the layers by irradiating theadhesive composition to effect curing.

Because the photocuring speeds are high using the present invention, thephotoinitiator composition can be used to advantage with photocurablecompositions that are dyed or pigmented or with compositions into whichlight penetration is limited, such as inks. Such compositions can beapplied to substrates and then irradiated. It is also possible to usethe present invention to rapidly and partially or completely curing ofphotocurable compositions to modify their viscosities.

Definitions

Unless otherwise indicated, the term “photoinitiator composition” usedin this application will refer to embodiments used in the presentinvention.

The terms “curing”, “photocuring”, and “polymerizing” are used herein tomean the combining for example, by covalent bonding, of large number ofsmaller molecules, such as monomers or oligomers, to form very largemolecules, that is, macromolecules or polymers, when irradiated withradiation such as ultraviolet (UV), visible, or infrared radiation. Themonomers can be combined to form only linear macromolecules or they canbe combined to form three-dimensional macromolecule, commonly referredto as crosslinked polymers. Thus, these terms include polymerization offunctional oligomers and monomers, or even crosslinkable polymers, intoa crosslinked polymer network.

The terms “unsaturated monomer,” “functional oligomer,” and“crosslinking agent” are used herein with their usual meanings and arewell understood by those having ordinary skill in the art.

The singular form of each component of the photoinitiator compositionand photocurable composition is intended also to include the plural thatis, one or more of the respective components.

The term “ethylenically unsaturated polymerizable material” is meant toinclude any unsaturated material having one or more carbon-to-carbondouble bonds (ethylenically unsaturated groups) capable of undergoingpolymerization. The term encompasses ethylenically unsaturatedpolymerizable monomers, oligomers, and crosslinkable polymers. Thesingular form of the term is intended to include the plural.Monofunctional monomers, oligomers, and multifunctional acrylates areexamples of unsaturated polymerizable compounds.

As used herein, the term “quantum yield” is used herein to indicate theefficiency of a photochemical process. More particularly, quantum yieldis a measure of the probability that a particular molecule will absorb aquantum of light during its interaction with a photon. The termexpresses the number of photochemical events per photon absorbed. Thus,quantum yields can vary from zero (no absorption) to 1.

The term “photosensitizer” is meant to refer to a light absorbingcompound used to enhance the reaction of a photoinitiator. Uponphotoexcitation, a photosensitizer leads to energy or electron transferto a photoinitiator.

The term photoinitiator refers to a compound that generates freeradicals. As noted above, photoinitiators can be classified as “Type I”(or photocleavage) photoinitiators and “Type II” (or H-abstraction)photoinitiators according to the pathways by which the effectiveinitiating radicals are generated.

“Actinic radiation” is any electromagnetic radiation that is capable ofproducing photochemical action and can have a wavelength of at least 150nm and up to and including 1250 nm, and typically at least 300 nm and upto and including 750 nm.

Photoinitiator Compositions

In their most simple form, the energy-efficient photoinitiatorcompositions comprise:

(a) at least one radiation-sensitive photoinitiator that absorbs actinicradiation and therefore produces free radicals,

(b) at least one organic phosphite, and

(c) at least one aldehyde.

Any organic phosphite is useful in the practice of this invention butparticularly useful organic phosphites are represented by the followingStructure (I):

(R′O)₃P   (I)

wherein the multiple R′ groups are the same or different substituted orunsubstituted alkyl groups or HO[{CH(R)}_(x)O]_(y) groups wherein themultiple R groups are the same or different and can be hydrogen atoms orsubstituted or unsubstituted alkyl groups, or two R′ groups can form asubstituted or unsubstituted cyclic aliphatic ring or fused ring system,x is a number at least 2 and up to and including 20, and y is at least 1and up to and including 20.

For example, the multiple R′ groups can be the same or different alkylgroups having 1 to 10 carbon atoms or HO[{CH(R)}_(x)O]_(y) groupswherein the multiple R groups are the same or different and can behydrogen atoms or substituted or unsubstituted alkyl or cycloalkylgroups, x is an integer of at least 2 and up to and including 10, and yis an integer of at least 1 and up to and including 10.

For example, the photoinitiator composition can comprise one or more oftrimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributylphosphite, triisobutyl phosphite, triamyl phosphite, trihexyl phosphite,trinonyl phosphite, tri-(ethylene glycol)phosphite, tri-(propyleneglycol)phosphite, tri(isopropylene glycol)phosphite, tri-(butyleneglycol)phosphite, tri-(isobutylene glycol)phosphite, tri-(pentyleneglycol)phosphite, tri-(hexylene glycol)phosphite, tri-(nonyleneglycol)phosphite, tri-(diethylene glycol)phosphite, tri-(triethyleneglycol)phosphite, tri-(polyethylene glycol)phosphite, tri-(polypropyleneglycol)phosphite, and tri-(polybutylene glycol)phosphite. Spiro organicphosphites represented by the following Structure (II) are also usefulin the present invention.

wherein the two R₁ groups are the same or different substituted orunsubstituted alkyl groups or HO[{CH(R)}_(x)O_(y) groups wherein themultiple R groups are the same or different and can be hydrogen atoms orsubstituted or unsubstituted alkyl groups, or the two R₁ groups can forma substituted or unsubstituted cyclic aliphatic ring or fused ringsystem, x is a number at least 2 and up to and including 20, and y is atleast 1 and up to and including 20.

In some embodiments, the photoinitiator composition includes two or moredifferent organic phosphites.

Any Type I or Type II photoinitiator that generates radicals either upondirect absorption of actinic radiation or by energy transfer fromphotosensitizers (described below) is useful in present invention. Suchphotoinitiators include but are not limited to, aryl ketones, such asa-hydroxy ketones, a-amino ketones, and mono- and bis(acyl)phosphineoxides. Examples of a-hydroxy and α-amino ketones photoinitiators aredisclosed for example in U.S. Pat. No. 4,347,111 (Gehlhaus et al.), U.S.Pat. No. 4,321,118 (Felder et al.), U.S. Pat. No. 4,672,079 (Li Bassi etal.), and U.S. Pat. No. 4,987,159 (Li Bassi et al.), and in WO 04/092287(Fuchs et al.). Some specific examples are2-hydroxy-2-methyl-1-phenyl-propanone (Darcur® 1173),1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure® 184),bis[4-(2-hydroxy-2-methylpropionyl)phenyl]methane (Irgacure® 127),2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-phenoxy]-phenyl}-2-methy-1-propan-1-one,(1-[4-(2-hydroxyethoxy)-phenyl]-2-10 hydroxy-2-methyl-1-propan-1-one)(Irgacure® 2959), and oligo[2-hydroxy2-methyl-1-[4(1-methyl)phenyl]propanone (Esacure® KIP 150), which can beobtained from Ciba Specialty Chemicals and Lamberti SpA.

α-Amino ketones, particularly those containing a benzoyl moiety,otherwise called a-amino acetophenones, for example(4-methylthio-benzoyl)-1-methyl-1-morpholinoethane (Irgacure® 907),(4-morpholinobenzoyl)-1-benzyl-1-dimethylaminopropane (Irgacure® 369),(4-morpholinobenzoyl)-1-(4-methylbenzyl)-1-dimethylaminopropane(Irgacure® 379),(4-(2-hydroxyethyl)aminobenzoyl)-1-benzyl-1-dimethylminopropane),2-benzyl-2-dimethylamino-1-(3,4-dimethoxyphenyl)butan-1-one, and4-aroyl-1,3-dioxolanes are also useful.

Other useful photoinitiators include benzoin alkyl ethers and benzilketals, phenylglyoxalic esters and derivatives thereof such asoxo-phenyl-acetic acid 2-(2-hydroxy-ethoxy)-ethyl ester, and dimericphenylglyoxalic esters such as oxo-phenyl-acetic acid1-methyl-2-[2-(2-oxo-2-phenyl-acetoxy)-propoxy]-ethyl ester (Irgacure®754).

Examples of useful oxime ester photoinitiators are disclosed in U.S.Pat. No. 3,558,309 (Laridon et al.), U.S. Pat. No. 4,255,513 (Laridon etal.), U.S. Pat. No. 6,596,445 (Matsumoto et al.), and U.S. Pat. No.4,202,697 (DeWinter et al.) and in U.S. Patent Application Publication2010/0188765 (Matsumoto et al.). Some specific examples are1,2-octanedione 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime) (Irgacure®OXE01), ethanone1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxim-e)(Irgacure® OXE02), and 9H-thioxanthene-2-carboxaldehyde9-oxo-2-(O-acetyloxime).

Per-esters photoinitiators are also useful in present invention. Suchcompounds include benzophenone tetracarboxylic per-esters as describedfor example in EP 126,541 (Takeshi et al.).

Examples of useful mono- and bis-acylphosphine oxides are also knownfrom U.S. Pat. No. 4,324,744 (Lechtken et al.), U.S. Pat. No. 4,737,593(Enrich et al.), and U.S. Pat. No. 6,020,528 (Leppard et al.), and GBPublication 2,259,704 (Koehler et al.). Some specific examples are2-4-6-(trimethylbenzoyl)diphenyl-phosphine oxide (Dartocur® TPO),bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide (Irgacure® 819),(2,4,6 trimethylbenzoyl)phenyl phosphinic acid ethyl ester (LucirinTPO-L® BASF), bis(2,4,6-trimethylbenzoyl)-2,4-dipentoxyphenyl-phosphineoxide, and trisacylphosphine oxides.

Useful ketosulfone photoinitiators are known from WO 00/031030(Meneguzzo et al.). WO 06/120212 (Romagnano et al.) and U.S. Pat. No.6,048,660 (Leppard et al.), U.S. Pat. No. 4,475,999 (Via), and U.S. Pat.No. 4,038,164 (Via) describe phenylglyoxylates as photoinitiators.Gottschalk et al. have disclosed borates, associated with ionic dyes, asuseful as photoinitiators in U.S. Pat. Nos. 4,772,530, 4,772,541, and5,151,520. In GB Publication 2,307,474 (Cunningham et al.) havedisclosed borates as photoinitiators. Metallocenes such astitanocene-based photoinitiators are in U.S. Pat. No. 5,008,302 (Huesleret al.) and U.S. Pat. No. 5,340,701 (Desobry).

Mixtures of photoinitiators from a single class of compounds, or fromtwo or more different classes of compounds, can be used if desired. Thetotal amount of photoinitiators in the photoinitiator composition isgenerally at least 2 weight %, or typically at least 60 weight % and upto and including 90 weight %, based on the total composition solids. Theweight ratio of organic phosphite to photoinitiator in thephotoinitiator composition is at least 0.5:1 and up to and including50:1, or typically of at least 1:1 and up to and including 10:1.

The aldehydes useful in the photoinitiator compositions include anycompounds having one or more aldehyde (—CHO) moieties. It would bereadily apparent to one skilled in the art that the chosen aldehydeshould not interfere with curing radiation, with radiation absorption bythe photoinitiator, and the basic chemistry of the photoinitiator. Mostof the aldehydes are alkyl and aryl aldehydes having one or morealdehyde moieties. For example, useful aldehydes include R″—CHOcompounds in which R″ is an alkyl or aryl group that is unsubstituted orsubstituted with one or more groups that do not adversely affect thebehavior of the aldehyde moieties. For example, aryl aldehydes can besubstituted or unsubstituted benzaldehydes and naphthaldehydes includingbut not limited to, 4-methoxybenzaldehyde, 4-methylbenzaldehyde,terephthalaldehyde, 2,5-dimethoxy-1,4-benzenedicarboxaldehyde, andnaphthalene-1,4-dicarboxaldehyde. Useful alkyl aldehydes include but arenot limited to compounds with substituted or unsubstituted alkyl groupshaving 1 to 20 carbon atoms in the alkyl group. As used herein, “alkylgroup” also include substituted or unsubstituted cycloalkyl groupshaving 5 to 10 carbon atoms in the ring. Examples of useful alkylaldehydes include but are not limited to, acetaldehyde, propionaldehyde,butyraldehyde, 2-methylbutyraldehyde, cyclohexanecarboxaldehyde, andcyclopentanecarboxaldehyde.

It is also possible that the “aldehyde” is an oligomeric or polymericcompound having recurring units wherein each unit comprises an aldehydemoiety and is represented for example by —(CH₂CH(CHO))—. Thus, in suchembodiments, the R″ group noted above is an oligomeric or polymericbackbone and the oligomer or polymer has multiple aldehyde moietiesalong the backbone.

In one embodiment, the aldehyde has a single aldehyde moiety and amolecular weight less than 300. In other embodiments, the aldehyde hasone or two aldehyde moieties and a molecular weight less than 500.

The amount of aldehyde in the photoinitiator composition is chosen inrelation to the amount of total organic phosphites. For example, themolar ratio of the organic phosphite to the aldehyde moieties in acomposition of this invention is at least 1:1 and up to and including4:1, or typically at least 1:1 and up to and including 3:1, althoughmore or less phosphite can be used if desired. In some embodiments, theorganic phosphite is present in a molar excess (greater than 1:1)compared to the aldehyde moieties in the composition.

An organic phosphite, for example as defined above in Structure (I), andan aldehyde present in the photoinitiator or photocurable composition isbelieved to react to form an organic phosphite-aldehyde adduct,following the following reaction equation:

This complexation of phosphite with aldehyde happens rapidly at roomtemperature [for example, see F. Ramirez, Pure Appl. Chem. 1964, 9(2),337-369] and results in reducing the unpleasant odor associated withmany organic phosphites. This is especially true for some commonlyavailable organic alkyl phosphites such as trimethyl phosphite andtriethyl phosphite. It is believed that the compositions of thisinvention can include certain quantities of the organicphosphite-aldehyde adduct as well as unreacted organic phosphite oraldehyde. Unreacted organic phosphites are particularly present whenthey are included in molar excess relative to the aldehyde moieties inthe composition. The organic phosphite-aldehyde adduct, in some cases,can react with another molecule of aldehyde to formtetraalkoxyphosphoranes. In some embodiments, R′ is a substituted orunsubstituted alkyl group and R″ is a substituted or unsubstitutedphenyl group. This modified composition can also contain non-reactedorganic phosphite especially if a molar excess of organic phosphite ispresent in the original photoinitiator composition. Thus, the modifiedcomposition can be prepared by mixing a suitable photoinitiator, anorganic phosphite, and an aldehyde at room temperature in a suitableorganic solvent. Examples of useful organic solvents include but are notlimited to, ethyl methyl ketone, ethyl acetate, chloroform, methylenechloride, acetonitrile, toluene, xylenes, hexane, heptanes, petroleumether, diethyl ether, and mixtures of two or more of these solvents. Themodified composition also can be prepared by mixing a suitablephotoinitiator, an organic phosphite, and an aldehyde directly with aphotocurable compound, which could also serve as the solvent for theresulting photocurable composition.

In many embodiments, the photoinitiator compositions further comprise aphotosensitizer for the photoinitiator. Photosensitizers useful inpresent invention include any compounds capable of transferring energyfrom its own lowest excited state after it has absorbed radiation, tothe photoinitiator. The driving force for this process depends upon thetriplet energy of photosensitizer, (E^(T))_(s), and the triplet energyof photoinitiator, (E^(T))_(p). Thus, for the energy transfer fromphotosensitizer to photoinitiator to take place the triplet energy ofphotosensitizer (E^(T))_(s) should to be greater or equal to the tripletenergy of photoinitiator, (E^(T))_(p). Even in cases where the tripletenergy of the photosensitizer is slightly lower than that ofphotoinitiator, energy transfer is feasible.

The amount of photosensitizer used in the photoinitiator compositionsdepends largely on its optical density at the wavelength(s) of radiationused to initiate curing. Solubility of the photosensitizer in aphotocurable composition can also be a factor. It is possible that thephotosensitizer is a covalently bound part of a photocurable compoundsuch as an acrylate. Either a photosensitizer bound in this manner or anon-bound photosensitizer with a low extinction coefficient can beutilized at relatively high levels to help facilitate the transfer of anelectron to the photoinitiator from a triplet photosensitizer (³S). Whencovalently attached to a polymeric photocurable compound, thephotosensitizer can be present in an amount of at least 0.01 and up toand including 10 weight % based on the total weight of thephotoinitiator. An example of such a covalently bound photosensitizer isa benzophenone moiety (that absorbs actinic radiation) that is bound toa photocurable material, or it can be attached to an inert polymericbinder. The amount of the photosensitizers is generally governed bytheir molar absorptivity or extinction coefficient. Photosensitizersthat are not bound to photocurable compounds or polymers can be presentin an amount of at least 1 and up to and including 10 weight %, based onthe total weight of photoinitiator.

The triplet energies of the photosensitizers useful in present inventionare known (for example see Handbook of Photochemistry, Eds. Steven L.Murov, Ian Carmichael, Gordon L. Hug, 1993, Marcel Dekker, Inc.).Energies for some photosensitizers or closely related analogs are alsodisclosed in other literature. Methods to experimentally measure tripletenergies are also commonly known in the literature [for example see J.Amer. Chem. Soc. 102, 2152 (1980) and J. Phys. Chem. 78, 196 (1974)].

Some useful photosensitizers absorb visible light or near ultravioletlight, for example at a wavelength of at least 250 nm and up to andincluding 450 nm. The ketocoumarins disclosed in Tetrahedron 38, 1203(1982) represent one class of such useful photosensitizers. Theketocoumarins described in U.K. Patent Publication 2,083,832 (Specht etal.) are also useful photosensitizers. The ketocoumarins exhibit verytriplet state generation efficiencies. Other classes of usefulphotosensitizers include but are not limited to, benzophenones,xanthones, thioxanthones, arylketones and polycyclic aromatichydrocarbons.

The weight ratio of the combination of organic phosphite and aldehyde(including any phosphite-aldehyde adducts) to photoinitiator tophotosensitizer in some photoinitiator compositions is at least0.1:1:0.1 and up to and including 50:1:1, or typically of at least10:1:0.5 and up to and including 50:2:1. In such embodiments, the molarratio of the organic phosphite to aldehyde moieties is at least 1:1 andtypically at least 2:1.

Photocurable Compositions

The photoinitiator composition is very useful in photocurablecompositions to provide polymerized or crosslinked compositions invarious forms including but not limited to, coatings, molded articles,printed patterns, fibers, laminates, inks, and varnishes.

Such photocurable compositions then comprise at least one photoinitiator(as described above), at least one organic phosphite such as thosedefined above using Structure (I), at least one aldehyde (as describedabove), and at least one photocurable compound that can be, for example,an ethylenically unsaturated polymerizable compound (or monomer) thathas at least one terminal ethylenically unsaturated group and is capableof forming a polymerized material such as a prepolymer or polymer usingphotoinitiated addition polymerization. As described above, thephotoinitiator is radiation-sensitive and absorbs actinic radiation andproduces free radicals.

Such photocurable compounds may be unsaturated monomers and oligomersexamples of which include ethylene, propylene, vinyl chloride,isobutylene, styrene, isoprene, acrylonitrile, acrylic acid, methacrylicacid, ethyl acrylate, ethyl methacrylate, methyl acrylate, methylmethacrylate, butyl acrylate, vinyl acrylate, allyl methacrylate,tripropylene glycol diacrylate and other diacrylates anddimethacrylates, various triacrylates and tri-methylacrylates,trimethylol propane ethoxylate acrylate, epoxy acrylates such as thereaction products of a bisphenol A epoxide with acrylic acid, polyetheracrylates such as the reaction products of acrylic acid with an adipicacid/hexanediol-based polyether, urethane acrylates such as the reactionproduct of hydroxypropyl acrylate withdiphenylmethane-4,4′-diisocyanate, and polybutadiene diacrylateoligomers.

In many embodiments, the photocurable compound is a mono- ormulti-functional acrylate (also intended to include methacrylates) thatis considered herein to be any material of any molecular weight that hasat least one ethylenically unsaturated group. Such acrylates can beethylenically unsaturated polymerizable monomers, oligomers, andcrosslinkable polymers. The acrylates can have multiple acrylate groups(for example diacrylates and triacrylates). In other embodiments, thephotocurable compounds are resins having a weight average molecularweight of at least 100,000.

Many of these embodiments of photocurable compositions can also includesone or more photosensitizers, as described above, that absorbappropriate actinic radiation and are raised to an active state duringphotocuring.

The photocurable composition can include one or more non-reactiveorganic solvents including but not limited to, ethyl methyl ketone,ethyl acetate, chloroform, methylene chloride, acetonitrile, toluene,xylenes, hexane, heptanes, petroleum ether, diethyl ether, and mixturesof two or more of these solvents. The photocurable compound itself canact also as the organic solvent and be present as the sole organicsolvent or in combination with one or more non-reactive organicsolvents. By “non-reactive”, I mean that the organic solvent does notreact with any of the components of the composition.

In addition, the photocurable composition can include other materials asdesired, such as pigments, extenders, amine synergists, and such otheradditives as are well known to those having ordinary skill in the art.Alternatively, these addenda can be added to the photocurablecomposition during photocuring.

With both organic phosphite and aldehyde present in the photocurablecomposition, some of both compounds can react to for the organicphosphite-aldehyde adduct described above but generally it is desired tohave a molar excess of organic phosphite so that unreacted organicphosphite is also present in the photocurable composition.

In the photocurable compositions, a photosensitizer for thephotoinitiator can be present in an amount of at least 0.1 weight % andup to and including 10 weight %, or at least 0.5 weight % and up to andincluding 5 weight %, or more typically at least 1 weight % and up toand including 2 weight %, of the photocurable composition.

The photoinitiator concentrations in the photocurable compositions canbe specified in terms of weight % of photoinitiator in per gram ofphotocurable compound (or acrylate). Typical concentrations ofphotoinitiator are at least 0.1 weight % and up to and including 20weight %, or typically at least 0.5 weight % and up to and including 10weight %, or more typically at least 0.5 weight % and up and including 5weight % of photocurable composition. The exact amount of photoinitiatorthat is used, as is commonly understood by one skilled in the art,depends largely on its molar absorptivity at the wavelength ofexcitation and the efficiency of radical generation.

In addition, the combination of organic phosphite(s) and aldehydes(including phosphite-aldehyde adducts) can be present in thephotocurable composition in an amount of at least 0.5 weight % and up toand including 20 weight %, typically at least 1 weight % and up to andincluding 10 weight %, or more typically at least 2 weight % and up toand including 10 weight % of the photocurable composition. The use oflarger amounts of organic phosphite is also possible. The relative molarratio of organic phosphite to aldehyde moieties is generally at least1:1, and a molar excess of organic phosphite is desirable in manyembodiments.

The photoinitiator compositions and photocurable compositions can beprovided in any form that is suitable for the various components orintended use. In most embodiments, the photoinitiator compositions andphotocurable compositions are in solid form such as powders, granules,or pressed tablets. In some embodiments, the photoinitiator compositionsand photocurable compositions are in liquid form, such as solutionscontaining solvents for solubilizing or dispersing the components. Instill other embodiments, the photocurable composition is in liquid formin which the photocurable compound (such as an acrylate) serves as thesolubilizing or dispersing solvent.

Methods of Photocuring and Uses thereof

The present invention is also directed to a method of generating freeradicals to affect photocuring, especially in oxygen-containingenvironments. The method of generating free radicals involves generatinga free radical by exposing the described photoinitiator compositions tosuitable actinic radiation. The exposure of the photoinitiatorcompositions to a radiation source triggers a photochemical process. Asstated above, the term “quantum yield” is used herein to indicate theefficiency of a photochemical process.

The photoinitiator composition absorbs photons of specific wavelength(s)and transfers the absorbed energy to one or more excitable portions ofthe composition. The excitable portion of the compositions absorbsenough energy to cause a bond breakage that generates one or more freeradicals. The efficiency with which radicals are generated with thephotoinitiators depends on quantum yield of the given photoinitiator.Thus, the photoinitiators can be employed in any situation whereradicals are required, such as described above for photocuring orphotopolymerization.

By way of illustration only, a photocurable composition (as describedabove) is prepared or provided and irradiated, for example, in thepresence of oxygen, to cause photocuring or polymerization of variousphotocurable compounds within the composition and used for coatings,inks, printed articles, photoresists, or providing any image.

The photocurable composition can be used to polymerize or cure aphotocurable compound by exposure to suitable radiation for a time andenergy sufficient for efficacious photocuring. The photocurable compoundcan be mixed with the photoinitiator compositions using any suitablemixing means known in the art, following which the mixture is irradiatedwith an amount of radiation. The amount of radiation sufficient topolymerize the compound is readily determinable by one of ordinary skillin the art, and depends upon the identity and amount of photoinitiatorcomposition, the identity and amount of the photocurable compound, theintensity and wavelength of the radiation, and the duration of exposureto the radiation. In some instances, photocuring can occur during themixing, or both during and after the mixing. For example, somephotocurable compositions can be partially cured, treated in somemanner, and then subjected to further curing.

The photoinitiating compositions can be used to prepare photocurablecompositions by simply mixing, under “safe light” conditions, thephotoinitiating composition, or individually, the photoinitiator, anoptional photosensitizer for the photoinitiator, an aldehyde, and anorganic phosphite compound, with a suitable photocurable acrylate orother photocurable compound. This mixing can occur in suitable inertsolvents if desired. Examples of suitable solvents include but are notlimited to, acetone, methylene chloride, and any solvent that does notreact appreciably with the phosphite, photoinitiator, aldehyde,photocurable compound, or photosensitizer.

A liquid organic material to be polymerized or photocured (such as anacrylate) can be used as the solvent for mixing, or it can be used incombination with another liquid. An inert solvent can be used also toaid in obtaining a solution of the materials and to provide suitableviscosity to the photocurable compositions for coatings, or othermaterials or operations. However, solvent-free photocurable compositionsalso can be prepared by simply dissolving the photoinitiator, theorganic phosphite, aldehyde, or photosensitizer in the organicphotocurable material with or without mild heating.

The present invention can be used to produce a film by forming thephotocurable composition into a film and irradiating the film with anamount of radiation sufficient to polymerize or cure the composition.Any film thickness can be produced as long as the photocurablecomposition sufficiently polymerizes upon exposure to radiation. Thisfilm can form an article for various purposes. The photocurablecomposition can be drawn into a film on a nonwoven web or on a fiber,thereby providing a cured coating on a nonwoven web or fiber. Any methodknown in the art for drawing the photocurable composition into a filmcan be used. The amount of radiation sufficient to photocure thephotocurable composition is readily determinable by one of ordinaryskill in the art, and depends upon the identity and amount ofphotoinitiator, the identity and amount of the photocurable compound,the thickness of the admixture, the intensity and wavelength of theradiation, and the duration of exposure to the radiation.

The present invention can also be used to provide adhesive compositionscomprising at least one unsaturated polymerizable or photocurablecompounds admixed with photoinitiator composition. Similarly, thepresent invention can be used to provide a laminated structure (orarticle) comprising at least two layers bonded together with thedescribed adhesive composition. In one embodiment, a laminate isproduced wherein at least one layer is a cellulosic or polyolefinnonwoven web or film. Accordingly, the present invention can be used toprovide a method of laminating a structure wherein a structure having atleast two layers with the described adhesive composition between thelayers is irradiated to polymerize or photocure the adhesivecomposition. It is to be understood that any substrates can be used inthe laminates as long as at least one of the substrates allowssufficient radiation to penetrate through the layer to enable theadmixture to polymerize to the desired extent. For example, such a layercan be transparent. Accordingly, any cellulosic or polyolefin nonwovenweb or film known in the art may be used as one of the layers so long asthey allow radiation to pass through. As described above, the amount ofradiation sufficient to photocure the adhesive composition would bereadily determinable by one of ordinary skill in the art, and dependsupon the identity and amount of photoinitiator, the identity and amountof the photocurable compound, the thickness of the adhesive composition,the identity and thickness of the layer, the intensity and wavelength ofthe radiation, and the duration of exposure to the radiation.

Further, the present invention can be used to prepare an article that isobtained from a photocurable coating comprising a photocurablecomposition that comprises at least one photoinitiator, at least oneorganic phosphite, at least one aldehyde, and at least one photocurablecompound. This photocurable coating can be disposed on a suitablesubstrate that is a coated or uncoated paper, metal, coated or uncoatedpolymeric film, ceramic, glass, or fabrics. For example, thephotocurable composition can be disposed onto a substrate as a varnishcoating that is this irradiated in a suitable manner. The photocurablecoating can also be cured in an imagewise pattern or uniformly.

The photocurable coating can be disposed on the substrate uniformly orin a pattern. For example, the photocurable coating can be disposed on,or alternatively applied to, the substrate in an imagewise pattern usingan imagewise patterning or imaging method including the use of a mask.Such articles include but are not limited to, printed circuit boardprecursors in which a photocured image or pattern to provide a printedcircuit board. In some embodiments used to provide articles of thisinvention, the photocurable composition includes the organic phosphitein a molar excess to the aldehyde groups in the composition.

Other articles can be formed from a photocurable composition as acoating, component, or pattern. Thus, a photocurable composition isprovided in the article, and the photocurable composition is suitablyirradiated to cure it, partially or uniformly. This article can includea substrate on which the photocurable composition is disposed, or thearticle can include the photocurable composition as the substrateitself. The irradiation of the article, or to form the article, isparticularly advantageous if carried out in the presence of oxygen.

Other articles are composed of already cured photocurable compositions.Thus, a precursor articles can be formed with a photocurablecomposition, and this precursor article is irradiated in a suitablemanner to form an article. For example, a precursor article is aphotoresist precursor that includes a uniform coating or a pattern ofthe photocurable composition. This photoresist precursor is thenirradiated in a suitable manner to (through a mask if a uniform coatingis used) to provide a desired photoresist.

As noted above, the photoinitiator composition can be used in a methodof photocuring a photocurable composition comprising:

mixing at least one photoinitiator, at least one organic phosphite, atleast one aldehyde, and at least one photocurable compound to form aphotocurable composition, and

irradiating the photocurable composition to provide a photocuredcomposition. The irradiating step is advantageously carried out in thepresence of oxygen. The photocurable composition can be coated (forexample, as a photocurable ink) onto a substrate (film, fiber, or moldedarticle) prior to irradiation, or during irradiation.

In some methods, the photocurable composition is partially cured duringthe irradiating step to provide a partially cured composition. Forexample, the photocurable composition can be jetted out of a nozzle(such as a photocurable ink) onto a substrate before partial curing fromthe irradiating step to modify the viscosity of the photocurablecomposition. This process can also comprise a step of further curing thepartially cured photocurable composition.

The irradiating step is carried out using radiation having a wavelengthof at least 100 nm and up to and including 1250 nm, and particularly ata wavelength of at least 100 nm and up to and including 1,000 nm. Thephotocuring radiation may be ultraviolet radiation, including nearultraviolet and far or vacuum ultraviolet radiation, visible radiation,and near infrared radiation. Desirably, the radiation will have awavelength of at least 100 nm and up to and including 900 nm, ortypically at least 100 nm and up to and including 700 nm. Usefulultraviolet radiation has a wavelength of from at least 100 rim and upto and including 400 nm. The radiation desirably will be incoherent,pulsed ultraviolet radiation from a dielectric barrier discharge excimerlamp or radiation from a mercury lamp. Other sources of radiation can beused.

In many embodiments, the photocurable composition is dissolved ordispersed in a solvent before the irradiating step. Alternatively, thephotocurable composition is mixed as a solution with at least onephotocurable compound acting as the solvent. In either of theseembodiments, the photocurable compound can be a photocurable acrylate.

Thus, the method can further comprise applying the photocurablecomposition to a substrate before the irradiating step. Alternatively,the method includes putting the photocurable composition into a moldbefore the irradiating step.

In these methods, the photocurable composition comprises thephotoinitiator (described above) in an amount of at least 6×10⁻⁷ and upto and including 6×10⁻² moles per gram of one or more photocurablecompounds (described above, such as acrylates). Moreover, thephotocurable composition can further include a photosensitizer(described above) that is present in an amount of at least 5×10⁻⁷ and upto and including 1×10⁻⁴ moles per gram of the one or more photocurablecompounds. The photocurable composition used in this method can comprisethe organic phosphite and aldehyde (described above) in amountsdescribed above. The one or more photocurable compounds can include aphotocurable monomeric, oligomeric, or polymeric acrylate. In someembodiments, the one or more photocurable compounds comprise aphotocurable acrylate that comprises a photosensitizer for thephotoinitiator.

Where an aldehyde is present in the photocurable composition, theorganic phosphite can be present in a molar excess relative to thealdehyde moieties, or a molar ratio of at least 1:1 and up to andincluding 4:1. For example, the aldehyde can be an alkyl or arylaldehyde having one or more aldehyde moieties and having a molecularweight less than 500.

The photoinitiator composition can be used in a method of imagingcomprising:

A) providing a photocurable composition comprising at least onephotoinitiator (described above), at least one organic phosphite(described above), at least one aldehyde (described above), and at leastone photocurable compound (described above, such as an acrylate) to forma photocurable composition, and

B) imagewise irradiating the photocurable composition to affect a curedimage.

The photocurable composition can be applied to a substrate prior to theimagewise irradiating step. Moreover, the imagewise irradiating step canbe carried out by irradiating the photocurable composition through amask image.

The photocurable composition can be applied to a substrate (describedabove) during the imagewise irradiating step. For example, thephotocurable composition can be applied to a metal substrate for use inproviding a printed circuit board or photoresist. If desired, thephotocurable composition further comprises a photosensitizer (describedabove) for the photoinitiator. Moreover, imagewise irradiating thephotocurable composition can be carried out in a pattern and thenon-cured portions of the photocurable composition can be removed bydevelopment. Useful developers would be readily apparent to a skilledworker and dependent upon the photocurable compound that is used. It isparticularly advantageous to carry out imagewise irradiating in thepresence of oxygen.

Evaluation of useful photoinitiator compositions as initiating systemsfor photopolymerization or photocuring can be carried out using anacrylate-based coating formulation (see Examples below). Irradiation toinitiate photocuring can be carried out using a filtered mercury lampoutput with or without band-pass filters. This is just one source ofuseful radiation. The efficiency of photopolymerization can bedetermined by the amount of photocured polymer retained after solventdevelopment, which leaves behind only the areas that had sufficientexposure to cause crosslinking of the photocurable acrylates. Thus, amore efficient photoinitiator composition can create more crosslinkedpolymer than a less efficient photoinitiator composition.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A method of photocuring a photocurable composition comprising:

mixing at least one photoinitiator, at least one organic phosphite, atleast one aldehyde, and at least one photocurable compound to form aphotocurable composition, and

irradiating the photocurable composition to provide a photocuredcomposition.

2. The method of embodiment 1 wherein the irradiating is carried out inthe presence of oxygen.

3. The method of embodiment 1 or 2 wherein the photocurable compositionis partially cured during the irradiating step to provide a partiallycured composition.

4. The method of embodiment 3 wherein the photocurable composition isjetted out of a nozzle before partial curing from the irradiating stepto modify the viscosity of the photocurable composition.

5. The method of embodiment 3 or 4 further comprising a step of furthercuring the partially cured composition.

6. The method of any of embodiments 1 to 5 wherein the irradiating stepis carried out using radiation having a wavelength of at least 100 nmand up to and including 1250 nm.

7. The method of any of embodiments 1 to 6 wherein the photocurablecomposition is dissolved or dispersed in a solvent before theirradiating step.

8. The method of any of embodiments 1 to 7 wherein the photocurablecomposition is mixed as a solution with at least one photocurablecompound acting as the solvent.

9. The method of any of embodiments 1 to 8 wherein the photocurablecompound is a photocurable acrylate.

10. The method of any of embodiments 1 to 9 further comprising applyingthe photocurable composition to a substrate before the irradiating step.

11. The method of any of embodiments 1 to 10 further comprising puttingthe photocurable composition into a mold before the irradiating step.

12. The method of any of embodiments 1 to 11 wherein the photocurablecomposition comprises the photoinitiator in an amount of at least 6×10⁻⁷and up to and including 6 x moles per gram of the photocurable compound.

13. The method of any of embodiments 1 to 12 wherein the organicphosphite is present in the photocurable composition in a molar ratio toaldehyde moieties of at least 1:1 and up to and including 4:1.

14. The method of any of embodiments 1 to 13 wherein the photocurablecomposition further comprises a photosensitizer that is present in anamount of at least 5×10⁻⁷ and up to and including 1×10⁻⁴ moles per gramof the photocurable compound.

15. The method of any of embodiments 1 to 14 wherein the photocurablecomposition further comprises a photosensitizer for the photoinitiatorthat is selected from the group consisting of ketocoumarins,benzophenones, xanthones, thioxanthones, arylketones, and polycyclicaromatic hydrocarbons.

16. The method of any of embodiments 1 to 15 wherein the organicphosphite is represented by the following Structure (I) or (II):

(R′O)₃P   (I)

wherein the multiple R′ groups are the same or different substituted orunsubstituted alkyl groups or HO[{CH(R)}_(x)O]_(y) groups wherein themultiple R groups are the same or different and can be hydrogen atoms orsubstituted or unsubstituted alkyl groups, or two R′ groups can form acyclic aliphatic ring or fused ring system,

wherein the two R₁ groups are the same or different substituted orunsubstituted alkyl groups or HO[{CH(R)}_(x)O]_(y) groups wherein themultiple R groups are the same or different and can be hydrogen atoms orsubstituted or unsubstituted alkyl groups, or the two R₁ groups can forma substituted or unsubstituted cyclic aliphatic ring or fused ringsystem, and

x is a number at least 2 and up to and including 20, and y is at least 1and up to and including 20.

17. The method of any of embodiments 1 to 16 wherein the organicphosphite is trimethyl phosphite, triethyl phosphite, tripropylphosphite, tributyl phosphite, triisobutyl phosphite, triamyl phosphite,trihexyl phosphite, trinonyl phosphite, tri-(ethylene glycol)phosphite,tri-(propylene glycol)phosphite, tri(isopropylene glycol)phosphite,tri-(butylene glycol)phosphite, tri-(isobutylene glycol)phosphite,tri-(pentylene glycol)phosphite, tri-(hexylene glycol)phosphite,tri-(nonylene glycol)phosphite, tri-(diethylene glycol)phosphite,tri-(triethylene glycol)phosphite, tri-(polyethylene glycol)phosphite,tri-(polypropylene glycol)phosphite, or tri-(polybutyleneglycol)phosphite.

18. The method of any of embodiments 1 to 17 wherein the photoinitiatoris one or more of a benzoin, aryl ketone, a-amino ketone, mono- orbis(acyl)phosphine oxide, benzoin alkyl ether, benzil ketal,phenylglyoxalic ester or derivatives thereof, oxime ester, per-ester,ketosulfone, phenylglyoxylate, borate, and metallocene.

19. The method of any of embodiments 1 to 18 wherein the aldehyde is analkyl or aryl aldehyde having one or more aldehyde moieties and having amolecular weight less than 500.

20. The method of any of embodiments 1 to 19 wherein the one or morephotocurable compounds comprises a photocurable acrylate that comprisesa photosensitizer for the photoinitiator.

21. A method of imaging comprising:

A) providing a photocurable composition comprising at least onephotoinitiator, at least one organic phosphite, at least one aldehyde,and at least one photocurable compound to form a photocurablecomposition, and

B) imagewise irradiating the photocurable composition to effect a curedimage.

22. The method of embodiment 21 further comprising applying thephotocurable composition to a substrate prior to the imagewiseirradiating step.

23. The method of embodiment 21 or 22 wherein the imagewise irradiatingstep is carried out through a mask image.

24. The method of any of embodiments 21 to 23 comprising applying thephotocurable composition to a substrate during the imagewise irradiatingstep.

25. The method of any of embodiments 21 to 24 wherein imagewiseirradiating the photocurable composition is carried out in a pattern andfurther comprising removing the non-cured portions of the photocurablecomposition by development.

26. The method of any of embodiments 21 to 25 wherein the imagewiseirradiating is carried out in the presence of oxygen.

The present invention is further described by the examples which follow.Such examples, however, are not to be construed as limiting in any wayeither the spirit or the scope of the present invention. In theexamples, all parts are by weight, unless stated otherwise.

The unexpected curing speed produced by the photoinitiating compositionsof the present invention is best understood by comparing theirperformance, when used with phosphite, to their performance when usedwithout one. A series of photocurable polymerizable mixtures containinginvention photoinitiating compositions were formulated and compared withphotocurable mixtures containing only the photoinitiator.

In all of the results shown below, the term “efficiency gain” refers tothe increased “speed” of curing that is represented by the ratio ofcuring energy dose of the comparative composition to the inventivecomposition. In addition, the term “curing degree” can be evaluated bythe extent of tackiness of the “cured” composition.

COMPARATIVE EXAMPLE 1

A non-inventive photocurable mixture was prepared by dissolvingIrgacure® 651 (1 weight %, 130 mg) in ethoxylated(20) trimethylolpropanetriacrylate (13 g, SR 415 from Sartomer). This photopolymerizablecomposition was then coated onto a glass plate and exposed in air tooutput from Hg light source. The cure efficiency was measured in termsof total dose required to attain crosslinking and the results aresummarized in TABLE I below.

COMPARATIVE EXAMPLE 2

Another non-inventive photocurable composition was prepared bydissolving triethyl phosphite (5 weight %, 0.650 g) and Irgacure® 651 (1weight %, 130 mg) in ethoxylated(20) trimethylolpropane triacrylate (13g, SR 415 from Sartomer). This photocurable mixture was then coated ontoa glass plate and exposed to light from output of an Hg light source inair. The cure efficiency was measured in terms of total dose required toattain complete crosslinking and the results are summarized in TABLE Ibelow.

TABLE I Photocuring Efficiency in Air Efficiency Dose mJ/cm² Gain CuringDegree Comparative Example 1 15 Poor-tacky (no phosphite) compositionComparative Example 2 3 5 times Good-little or (5 weight % phosphite) notackiness

These results clearly show that photocurable composition used inComparative Example 2 is at least 5 times more efficient than thephotocurable composition used in Comparative Example 1.

COMPARATIVE EXAMPLE 3

A non-inventive photocurable mixture was prepared by dissolvingIrgacure® 819 (1 weight %, 140 mg) in ethoxylated(20) trimethylolpropanetriacrylate (14 g, SR 415 from Sartomer). This photocurable compositionwas then coated onto a glass plate and exposed in air to output from anHg light source. The cure efficiency was measured in terms of total doserequired to attain crosslinking and the results are summarized in TABLEII below.

COMPARATIVE EXAMPLE 4

A photocurable composition was prepared by dissolving triisopropylphosphite (5 weight %, 0.700 g) and Irgacure® 819 (1 weight %, 140 mg)in ethoxylated(20) trimethylolpropane triacrylate (14 g, SR 415 fromSartomer). This photocurable composition was then coated onto a glassplate and exposed to light from an Hg light source in air. Cureefficiency was measured in terms of total dose required to attaincomplete crosslinking and the results are summarized in TABLE II below.

COMPARATIVE EXAMPLE 5

A photocurable composition was prepared by dissolving triisopropylphosphite (10 weight %, 1.4 g) and Irgacure® 819 (1 weight %, 140 mg) inethoxylated(20) trimethylolpropane triacrylate (14 g, SR 415 fromSartomer). This photocurable composition was then coated onto a glassplate and exposed to light from an Hg light source in air. Cureefficiency was measured in terms of total dose required to attaincomplete crosslinking. The results are summarized in TABLE II below.

TABLE II Photocuring Efficiency in Air Efficiency Dose mJ/cm² GainCuring Degree Comparative Example 3 20 Poor-tacky (no phosphite)composition Comparative Example 4 0.4  50 times Good-little or (5 weight% phosphite) no tackiness Comparative Example 5 0.2 100 timesGood-little or (10 weight % phosphite) no tackiness

These results also show the considerable improvement in photocuring inair when the photocurable compositions of Comparative Examples 4 and 5was used compared to the Comparative Example 3 composition that did notcontain a phosphite.

COMPARATIVE EXAMPLE 6

A photocurable composition was prepared by dissolving Irgacure® 369 (1weight %, 140 mg) in ethoxylated(20) trimethylolpropane triacrylate (14g, SR 415 from Sartomer). This photocurable compound was then coatedonto a glass plate and exposed in air to output from an Hg light source.The cure efficiency was measured in terms of total dose required toattain crosslinking and the results are summarized in TABLE III below.

COMPARATIVE EXAMPLE 7

A photocurable composition was prepared by dissolving triethyl phosphite(5 weight %, 0.700 g) and Irgacure® 369 (1 weight %, 140 mg) inethoxylated(20) trimethylolpropane triacrylate (14 g, SR 415 fromSartomer). This photocurable composition was then coated onto a glassplate and exposed to light from an Hg light source in air. Cureefficiency was measured in terms of total dose required to attaincomplete crosslinking and the results are summarized in TABLE III below.

TABLE III Photocuring Efficiency in Air Efficiency Dose mJ/cm² GainCuring Degree Comparative Example 6 42 Poor-tacky (no phosphite)composition Comparative Example 7 2 21 times Good-little or (5 weight %phosphite) no tackiness

These results also show the considerable improvement in photocuring inair when the photocurable composition of Comparative Example 7 was usedcompared to the Comparative Example 6 composition that did not contain aphosphite.

COMPARATIVE INVENTION 8 Black Photocurable Ink

Black Pearl 880 carbon black pigment (Degussa, 4 weight %, 0.4 g),Solsperse® 3900 dispersant (Lubrizol, 2 weight %, 0.2 g) andpropoxylated neopentyl glycol diacrylate SR9003 (Sartomer, 34 weight %3.4 g) were ball milled (2 mm diameter ceramic beads). After ballmilling the dispersion, additional SR9003 (Sartomer, 45 weight %, 4.5 g)and polyester acrylate CN2283 (Sartomer, 5 weight %, 0.5 g) were addedto the carbon black dispersion. The particle size of the carbon blackpigment was about 300 nm. A mixture of photoinitiators, Genocure BDMM(Rahn USA Corp., 4 weight %, 0.4 g), Genocure EHA (Rahn USA Corp., 2.5weight %, 0.25 g), Genocure ITX (Rahn USA Corp., 1 weight %, 0.1 g), andGenocure PBZ (Rahn USA Corp., 2.5 weight %, 0.25 g), was added into thepigment dispersion and stirred overnight in dark. A test patch (about1μm thick) was coated onto a glass plate and exposed to curing radiation(light) in air. The cure efficiency of the ink patch was evaluated basedon its tackiness after light exposure. The results are summarized inTABLE IV below.

INVENTION EXAMPLE 1 Preparing Black Photocurable Ink

Black Pearl 880 carbon black pigment (Degussa, 4 weight %, 0.4 g),Solsperse® 3900 dispersant (Lubrizol, 2 weight %, 0.2 g) andpropoxylated neopentyl glycol diacrylate SR9003 (Sartomer, 34 weight %3.4 g) were ball milled (using 2 mm diameter ceramic beads). After ballmilling, additional SR9003 (Sartomer, 45 weight %, 4.5 g) and polyesteracrylate CN2283 (Sartomer, 5 weight %, 0.5 g) were added to the pigmentdispersion. The average particle size of the carbon black pigment wasabout 300 nm. A mixture of photoinitiators, Genocure BDMM (Rahn USACorp., 4 weight %, 0.4 g), Genocure EHA (Rahn USA Corp., 2.5 weight %,0.25 g), Genocure ITX (Rahn USA Corp., 1 weight %, 0.1 g), and GenocurePBZ (Rahn USA Corp., 2.5 weight %, 0.25 g), was added to the carbonblack dispersion and stirred overnight in the dark. Triethylphosphite (5weight %) and 4-methoxybenzaldehyde (4 weight %) were then added to thecarbon black dispersion and mixed thoroughly. A test patch (about 1 μmthick) was coated on a glass plate to provide a useful article and thenexposed to curing radiation in the presence of oxygen (in air). The cureefficiency of the ink patch was evaluated based on tackiness of the inkpatch after irradiation. The results are summarized in TABLE IV below.

TABLE IV Efficiency Dose mJ/cm² Gain Curing Degree Comparative Invention8 (no 5500 Very poor phosphite or aldehyde) curing, patch was very tackyInvention Example 1 200 28 times Good-little or (phosphite & aldehyde)no tackinessThe results shown in TABLE IV clearly show considerable improvement inthe photocuring of a black-pigmented photocurable ink in air when thephotocurable composition contained an organic phosphite and aldehydeaccording to this invention.

COMPARATIVE EXAMPLE 9 Yellow Photocurable Ink

Yellow pigment PY-185 (BASF, 4 weight %, 0.4 g), Solsperse® 13240dispersant (Lubrizol, 4 weight %, 0.4 g), and 2-ethylhexyl acrylate(Aldrich, 30.1 weight % 3.1 g) were ball milled (using 2 mm diameterceramic beads). After ball milling, additional SR9003 (Sartomer, 46weight %, 4.6 g) and polyester acrylate CN2283 (Sartomer, 5 weight %,0.5 g) were added to the pigment dispersion. The average particle sizeof the yellow pigment was about 300 mm A mixture of photoinitiators,Genocure BDMM (Rahn USA Corp., 4 weight %, 0.39 g), Genocure EHA (RahnUSA Corp., 2.5 weight %, 0.26 g), Genocure ITX (Rahn USA Corp., 1 weight%, 0.1 g), and Genocure PBZ (Rahn USA Corp., 2.5 weight %, 0.25 g), wasadded to the pigment dispersion that was then stirred overnight in thedark. A test patch (about 1 μm thick) was coated on a glass plate toprovide an article and exposed to curing radiation in air. The cureefficiency of ink patch was evaluated based on the tackiness of theyellow ink patch after irradiation. The results are summarized in TABLEV below.

INVENTION EXAMPLE 2 Preparation of Yellow Photocurable Ink

Yellow pigment PY-185 (BASF, 4 weight %, 0.4 g), Solsperse® 13240dispersant (Lubrizol, 4 weight %, 0.4 g), and 2-ethylhexyl acrylate(Aldrich, 30.1 weight % 3.1 g) were ball milled (using 2 mm diameterceramic beads). After ball milling, additional SR9003 (Sartomer, 46weight %, 4.6 g) and polyester acrylate CN2283 (Sartomer, 5 weight %,0.5 g) were added to the pigment dispersion. The average particle sizeof the yellow pigment was about 300 nm. A mixture of photoinitiators,Genocure BDMM (Rahn USA Corp., 4 weight %, 0.39 g), Genocure EHA (RahnUSA Corp., 2.5 weight %, 0.26 g), Genocure ITX (Rahn USA Corp., 1 weight%, 0.1 g), and Genocure PBZ (Rahn USA Corp., 2.5 weight %, 0.25 g), wasadded to the pigment dispersion that was then stirred overnight in thedark. Triethylphosphite (5 weight %) and 4-methoxybenzaldehyde (4 weight%) were added and mixed thoroughly. A test patch (about 1 μm thick) wascoated onto a glass plate to provide a useful article and then exposedto curing radiation in air. The cure efficiency of the photocurable inkpatch was evaluated based on tackiness of the ink patch afterirradiation. The results are summarized in TABLE V below.

TABLE V Efficiency Dose mJ/cm² Gain Curing Degree Comparative Example 96500 Very poor (no phosphite or aldehyde) curing. Patch very tackyInvention Example 2 190 34 times Good-little or (phosphite & aldehyde)no tackinessThe results shown in TABLE V clearly show considerable improvement usingthe photocurable ink of this invention when cured in the presence ofoxygen compared with the comparative photocurable ink.

COMPARATIVE EXAMPLE 10 Photoresist Article

Poly(methyl methacrylate-co-methacrylic acid) (50:50, Eudragit® L100,acid value of 300-330 mg KOH per g, 3 g, ˜16 weight %) was dissolved in1-methoxy-2-propanol (10 g, ˜54 weight %). To this solution, Irgacure®369 (CIBA, ˜2.7 weight %, 0.5 g) was added and mixed thoroughly.Dipentaerythritol pentaacrylate (SR 399, 16 weight %, 3 g) andethoxylated trimethylolpropane triacrylate (SR9035, ˜11 weight %, 2 g)were added to the resulting formulation that was mixed completely toprovide a photocurable negative-working photoresist composition. Thiscomposition was spin-coated onto a glass plate and dried at 70° C. on ahot plate for 5 minutes and then exposed to UV light through a steptablet (14 steps, each step corresponding to 0.15 density change). Afterexposure, the article was developed in aqueous Na₂CO₃ (1 weight %)solution for 45 seconds. The cure efficiency was evaluated based onnumber of steps developed for a given dose of light exposure.

INVENTION EXAMPLE 3 Photoresist Article

Poly(methyl methacrylate-co-methacrylic acid) (50:50, Eudragit® L100,acid value of 300-330 mg KOH per g, 3 g, ˜16 weight %) was dissolved in1-methoxy-2-propanol (10 g, ˜54 weight %). To this solution, Irgacure369 (CIBA, ˜2.7 weight %, 0.5 g) was added and mixed thoroughly.Dipentaerythritol pentaacrylate (SR 399, 16 weight %, 3 g) andethoxylated trimethylolpropane triacrylate (SR9035, ˜11 weight %, 2 g),a mixture of 4-methoxybenzaldehyde (1.0 g, ˜5 weight %) andtriethylphosphite (1.0 g, ˜5 weight %) were added to the resultingformulation that was mixed completely to provide an inventivephotocurable negative-working photoresist composition. This compositionwas spin-coated onto a glass plate and dried at 70° C. on a hot platefor 5 minutes and then exposed to UV light through a step tablet (14steps, each step corresponding to 0.15 density change). After exposure,the article was developed in aqueous Na₂CO₃ (1 weight %) solution for 45seconds. The cure efficiency was evaluated based on number of stepsdeveloped for a given dose of light exposure.

TABLE VI Dose # of Steps mJ/cm² Developed Efficiency Gain ComparativeExample 10 510 10 (Photoresist with no phosphite or aldehyde) InventionExample 3 170 10 3 times (Photoresist with phosphite & aldehyde, total10 wt. %)

The results shown in TABLE VI clearly demonstrate that compared to thephotoresist of Comparative Example 9, the speed of the photoresist inInventive Example 3 was increased by a factor of 3. Thus, thephotoinitiator composition and photocurable composition of thisinvention can provide significant curing efficiency improvements.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A method of photocuring a photocurable composition comprising: mixingat least one photoinitiator, at least one organic phosphite, at leastone aldehyde, and at least one photocurable compound to form aphotocurable composition, and irradiating the photocurable compositionto provide a photocured composition.
 2. The method of claim 1 whereinthe irradiating is carried out in the presence of oxygen.
 3. The methodof claim 1 wherein the photocurable composition is partially curedduring the irradiating step to provide a partially cured composition. 4.The method of claim 3 wherein the photocurable composition is jetted outof a nozzle before partial curing from the irradiating step to modifythe viscosity of the photocurable composition.
 5. The method of claim 3further comprising a step of further curing the partially curedcomposition.
 6. The method of claim 1 wherein the irradiating step iscarried out using radiation having a wavelength of at least 100 nm andup to and including 1250 nm.
 7. The method of claim 1 wherein thephotocurable composition is dissolved or dispersed in a solvent beforethe irradiating step.
 8. The method of claim 1 wherein the photocurablecomposition is mixed as a solution with at least one photocurablecompound acting as the solvent.
 9. The method of claim 1 wherein thephotocurable compound is a photocurable acrylate.
 10. The method ofclaim 1 further comprising applying the photocurable composition to asubstrate before the irradiating step.
 11. The method of claim 1 furthercomprising putting the photocurable composition into a mold before theirradiating step.
 12. The method of claim 1 wherein the photocurablecomposition comprises the photoinitiator in an amount of at least 6×10⁻⁷and up to and including 6×10⁻² moles per gram of the photocurablecompound.
 13. The method of claim 1 wherein the organic phosphite ispresent in the photocurable composition in a molar ratio to aldehydemoieties of at least 1:1 and up to and including 4:1.
 14. The method ofclaim 1 wherein the photocurable composition further comprises aphotosensitizer that is present in an amount of at least 5×10⁻⁷ and upto and including 1×10⁻⁴ moles per gram of the photocurable compound. 15.The method of claim 1 wherein the photocurable composition furthercomprises a photosensitizer for the photoinitiator that is selected fromthe group consisting of ketocoumarins, benzophenones, xanthones,thioxanthones, arylketones, and polycyclic aromatic hydrocarbons. 16.The method of claim 1 wherein the one or more photocurable compoundscomprises a photocurable acrylate that comprises a photosensitizer forthe photoinitiator.
 17. The method of claim 1 wherein the organicphosphite is represented by the following Structure (I) or (II):(R′O)₃P   (I) wherein the multiple R′ groups are the same or differentsubstituted or unsubstituted alkyl groups or HO[{CH(R)}_(x)O]_(y) groupswherein the multiple R groups are the same or different and can behydrogen atoms or substituted or unsubstituted alkyl groups, or two R′groups can form a cyclic aliphatic ring or fused ring system,

wherein the two R₁ groups are the same or different substituted orunsubstituted alkyl groups or HO[{CH(R)}_(x)O]_(y) groups wherein themultiple R groups are the same or different and can be hydrogen atoms orsubstituted or unsubstituted alkyl groups, or the two R₁ groups can forma substituted or unsubstituted cyclic aliphatic ring or fused ringsystem, and x is a number at least 2 and up to and including 20, and yis at least 1 and up to and including
 20. 18. The method of claim 1wherein the organic phosphite is trimethyl phosphite, triethylphosphite, tripropyl phosphite, tributyl phosphite, triisobutylphosphite, triamyl phosphite, trihexyl phosphite, trinonyl phosphite,tri-(ethylene glycol)phosphite, tri-(propylene glycol)phosphite,tri(isopropylene glycol)phosphite, tri-(butylene glycol)phosphite,tri-(isobutylene glycol)phosphite, tri-(pentylene glycol)phosphite,tri-(hexylene glycol)phosphite, tri-(nonylene glycol)phosphite,tri-(diethylene glycol)phosphite, tri-(triethylene glycol)phosphite,tri-(polyethylene glycol)phosphite, tri-(polypropylene glycol)phosphite,or tri-(polybutylene glycol)phosphite.
 19. The method of claim 1 whereinthe photoinitiator is one or more of a benzoin, aryl ketone, a-aminoketone, mono- or bis(acyl)phosphine oxide, benzoin alkyl ether, benzilketal, phenylglyoxalic ester or derivatives thereof, oxime ester,per-ester, ketosulfone, phenylglyoxylate, borate, and metallocene. 20.The method of claim 1 wherein the aldehyde is an alkyl or aryl aldehydehaving one or more aldehyde moieties and having a molecular weight lessthan
 500. 21. A method of imaging comprising: A) providing aphotocurable composition comprising at least one photoinitiator, atleast one organic phosphite, at least one aldehyde, and at least onephotocurable compound to form a photocurable composition, and B)imagewise irradiating the photocurable composition to effect a curedimage.
 22. The method of claim 21 further comprising applying thephotocurable composition to a substrate prior to the imagewiseirradiating step.
 23. The method of claim 21 wherein the imagewiseirradiating step is carried out through a mask image.
 24. The method ofclaim 21 comprising applying the photocurable composition to a substrateduring the imagewise irradiating step.
 25. The method of claim 21wherein the photocurable composition further comprises a photosensitizerfor the photoinitiator.
 26. The method of claim 21 wherein imagewiseirradiating the photocurable composition is carried out in a pattern andfurther comprising removing the non-cured portions of the photocurablecomposition by development.
 27. The method of claim 21 wherein theimagewise irradiating is carried out in the presence of oxygen.